In general, an image processing apparatus such as an image forming apparatus includes a photosensitive drum having electrostatic latent images formed thereon, a process cartridge having a developing roller for supplying toner to the photosensitive drum, and a toner cartridge (developer cartridge) having toner accommodated therein. As an example of the image forming apparatus, JP-A-9-319202 discloses a configuration including a supply opening for supplying toner in a toner cartridge to a developing chamber, a toner cartridge having formed therein a return opening for returning toner from the developing chamber to the inside of the toner cartridge, an agitator having blades for agitating the interior of the toner cartridge, and an auger capable of conveying toner within the developing chamber at a supply opening side toward a return opening side. In the image forming apparatus, when the agitator is rotated, the blades of the agitator are rotated so that the blades pass through a position opposite the supply opening from the below to the above, whereby the toner accumulated in the lower half portion of the toner cartridge is pushed upward by the blades of the agitator to be delivered through the supply opening at the above and is discharged through the supply opening. The toner is then conveyed toward the return opening side by the auger and circulated in such a manner that the toner is returned back through the return opening into the toner cartridge. Therefore, fresh toner can be always supplied to the developing chamber from the cartridge.